CN113281166A  Novel test method for measuring hoop elasticity modulus and Poisson's ratio of composite pipe  Google Patents
Novel test method for measuring hoop elasticity modulus and Poisson's ratio of composite pipe Download PDFInfo
 Publication number
 CN113281166A CN113281166A CN202110366444.7A CN202110366444A CN113281166A CN 113281166 A CN113281166 A CN 113281166A CN 202110366444 A CN202110366444 A CN 202110366444A CN 113281166 A CN113281166 A CN 113281166A
 Authority
 CN
 China
 Prior art keywords
 arc
 strain
 test piece
 tensile
 test
 Prior art date
 Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
 Granted
Links
Images
Classifications

 G—PHYSICS
 G01—MEASURING; TESTING
 G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
 G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
 G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces

 G—PHYSICS
 G01—MEASURING; TESTING
 G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
 G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
 G01N2203/0001—Type of application of the stress
 G01N2203/0003—Steady

 G—PHYSICS
 G01—MEASURING; TESTING
 G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
 G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
 G01N2203/0014—Type of force applied
 G01N2203/0016—Tensile or compressive
 G01N2203/0017—Tensile

 G—PHYSICS
 G01—MEASURING; TESTING
 G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
 G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
 G01N2203/0058—Kind of property studied
 G01N2203/0069—Fatigue, creep, strainstress relations or elastic constants
 G01N2203/0075—Strainstress relations or elastic constants

 G—PHYSICS
 G01—MEASURING; TESTING
 G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
 G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
 G01N2203/02—Details not specific for a particular testing method
 G01N2203/06—Indicating or recording means; Sensing means
 G01N2203/067—Parameter measured for estimating the property
 G01N2203/0676—Force, weight, load, energy, speed or acceleration

 G—PHYSICS
 G01—MEASURING; TESTING
 G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
 G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
 G01N2203/02—Details not specific for a particular testing method
 G01N2203/06—Indicating or recording means; Sensing means
 G01N2203/067—Parameter measured for estimating the property
 G01N2203/0682—Spatial dimension, e.g. length, area, angle
Abstract
The invention discloses a novel test method for measuring the hoop elasticity modulus and Poisson's ratio of a composite pipe, which is called as an arc test piece tensile test method. The method comprises the steps of measuring the circumferential elasticity modulus and Poisson ratio of the composite pipe by tensioning an arc test piece cut along the circumferential direction of the composite pipe, wherein two wedgeshaped selflocking clamps for fixing the end part of the arc test piece are respectively connected with a tensile testing machine through a specially designed oneway hinge and are used for absorbing outofplane bending deformation of the arc test piece in the initial stage of the test. In addition, the test method provides specific and clear regulations on the preparation of arcshaped test pieces, a tensile test device, a tensile loading system, a calculation method of the hoop elastic modulus and the Poisson ratio, the application range of the test method and the like. The invention has simple operation, accurate measurement result and wide applicability, and belongs to the technical field of fiber reinforced composite material tensile test.
Description
Technical Field
The invention relates to the technical field of fiber reinforced composite material testing, in particular to a novel testing method for measuring the annular elastic modulus and Poisson's ratio of a fiber reinforced composite material pipe.
Background
Fiber reinforced composite materials have been widely used in civil engineering as a concrete constraining material in recent years due to their high specific strength and excellent corrosion resistance, among which the most typical applications are: the composite pipe constrains the concrete column. Wherein, the composite material pipe can be manually manufactured by a wet paving method, and can also be directly manufactured by a composite material winding pipe. In view of production automation and good quality control of the filament winding technology, and convenience of construction, the composite winding pipe is the best choice among newlybuilt composite confined concrete columns.
In composite tube confined concrete columns, the fibre lay direction is typically at an angle of approximately 90 degrees to the tube axis, which means: under the action of the axial pressure, the transverse expansion of the concrete can be effectively restrained by the fibers which are arranged in the approximate annular direction, so that the strength and the ductility of the member are effectively improved.
The mode of the composite pipe for restraining the concrete column from being damaged under pressure is basically characterized in that the fibers of the composite pipe are broken along the annular direction, and the concrete is crushed. Therefore, for the composite pipe, the tensile properties in the hoop direction (including the hoop ultimate tensile strain, the hoop modulus of elasticity and the poisson ratio), especially the hoop modulus of elasticity, are decisively influenced on the stress performance of the composite pipe for restraining concrete. In the test method for measuring the elastic modulus of the composite material, besides the traditional straight strip sheet tensile test, split disc test and hydrostatic test, students in various countries around the world also put forward various test methods, but the existing methods have certain limitations in practical use, and particularly on the problem of measuring the circular elastic modulus of the composite material pipe, an accurate and convenient solution is still not available, and needs to be improved and developed. In order to solve the problem, the patent provides a simple and feasible test method aiming at measuring the annular elastic modulus and the Poisson ratio of the composite pipe, and has reliable results and wide applicability according to the existing technical conditions.
Tensile test measurement of fiberreinforced composite Material in straight strip form tensile properties measurements are well described in many national and regional test specifications, such as Standard test method for tensile Properties of Polymerbased composites [ ASTM D3039/D3039M14(2014) ], Standard test method for tensile Properties of fiberreinforced composites for civil engineering Reinforcement [ ASTM D7565/D7565M10 (2017) ], test method for tensile Properties of oriented fiberreinforced Polymerbased composites [ GB/T3354 (2014) ], test method for elastic constants of fiberreinforced composites [ GB/T32376 (2015) ], and so forth. However, this test method is mainly directed to continuous unidirectional fiber reinforced composite flat plates and cannot be used for composite wound tubes. For the composite pipe manually manufactured by the wet laying method, although a straight stripshaped sheet material test piece with the same material and the same laying layer can be manufactured for a tensile test, the tensile property measured by the straight stripshaped sheet material tensile test may overestimate the actual property expressed by the composite material in the composite material constraint concrete due to the difference of the curvatures of the two and the difference of the manufacturing methods.
In comparison, the splitdisk test adopts an annular test piece, relatively completely maintains the original shape of the pipe, and is widely applied to the measurement of the hoop tensile property of the composite pipe, such as the standard test method for the apparent hoop tensile strength of plastic or reinforced plastic pipes [ ASTM D229016(2016) ] and the test method for the apparent initial hoop tensile strength of glass fiber reinforced thermosetting plastic pipes in plastic pipeline systems [ ISO 8521(2009) ]. In the split disk test, in order to reduce the adverse effect of the friction force between the test piece and the split disk on the test result, the test section of the annular test piece should be as close as possible to the gap between the two semicircular split disks. However, as the tensile force is applied, the two split discs are gradually separated, and an unavoidable bending phenomenon occurs on a test section of the test piece, so that the accurate hoop elastic modulus and hoop tensile limit strain of the composite pipe cannot be obtained. In order to solve this problem, many improvements have been proposed for the splitdisk test method, such as moving the test section of the test piece away from the gap of the split disk to eliminate the influence of the bending of the test piece on the test result, but such a process brings another problem: the friction force between the test piece and the splitting disc enables tensile stress gradients distributed along the circumferential direction to be generated on the test piece, so that accurate tensile stress of a test section cannot be obtained, and accurate hoop tensile performance of the composite pipe cannot be measured.
Theoretically, if the influence of adverse factors such as bending and friction of the annular test piece on the determination of the hoop tensile property of the composite pipe is to be eliminated, the composite pipe internal pressure test is the best choice. The basic principle of the composite pipe internal pressure test is consistent with the ' test method for determining the fracture time under continuous internal pressure of a plastic pipeline systemglass fiber reinforced thermosetting plastic pipe ' (ISO 8521(2009) '), and the composite pipe is subjected to internal pressure application by water, oil or other liquid so as to realize annular stretching of the composite pipe. The composite pipe internal pressure test method ensures the longitudinal integrity of the test piece on one hand, and on the other hand, the composite pipe expands uniformly under the action of internal pressure, and the stress state of the composite pipe is similar to that of composite pipe confined concrete, so that the measured annular elastic modulus and Poisson ratio of the composite pipe are very reliable. However, the internal pressure test has the biggest problems that: in order to normally apply water pressure or oil pressure to the inner wall of the pipeline, it is necessary to ensure that the liquid does not leak during the pressurization process, so the sealing device at the end part is important; particularly for composite pipes with high strength and relatively small diameterthickness ratio, high internal pressure needs to be applied to the composite pipes to obtain accurate annular material performance data. In addition, while considering the sealing effect, it is necessary to eliminate the adverse effect of the stress generated in the axial direction of the test piece due to the end seal on the test result. To solve the above two problems, the end sealing device for the internal pressure test is often designed to be complicated. In addition, the tube diameter and thickness of the composite material wound tube produced industrially or the composite material tube produced manually by a wetlaying method have certain dispersion, which often leads to the failure of the standardized sealing device in the internal pressure test.
In summary, it can be known from the analysis of the prior art that the conventional test method for measuring the circumferential material performance of the composite pipe mainly has the following three problems, so that the method cannot be applied to measuring the circumferential elastic modulus of the composite pipe:
(1) the straight stripshaped sheet tensile test is only suitable for measuring the relevant performance of the composite flat plate and cannot solve the problem that the composite pipe has radian along the annular direction;
(2) the problem of bending or friction force which cannot be avoided in the split disc test causes a large error of the measured annular elastic modulus of the composite pipe;
(3) the test device for the internal pressure test is complicated and has poor applicability to the size deviation of the composite pipe, so that the test device is difficult to popularize and apply in practical projects.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a novel test method for measuring the circumferential elastic modulus and the poisson ratio of a composite pipe, aiming at solving the problems of inaccurate measurement, inconvenient operation and poor applicability of the circumferential elastic modulus and the poisson ratio of the composite pipe in the prior art.
The technical scheme adopted by the invention for solving the technical problem is as follows:
a novel test method for measuring the hoop elasticity modulus and Poisson's ratio of a composite pipe is used for stretching an arcshaped test piece, and the method comprises the following steps: the tested arcshaped test piece is directly cut along the circumferential direction of the composite pipe, and a strain gauge is pasted; two ends of the arcshaped test piece are respectively clamped on the wedgeshaped selflocking clamp; the wedgeshaped selflocking clamp is connected with a tensile testing machine through a oneway hinge so as to realize the free rotation of the arcshaped test piece around the oneway hinge steel shaft in the tensile process; the test comprises two stages in total; first stage of the experiment: under the stretching action, the outofplane bending of the arcshaped test piece is gradually absorbed until the arcshaped test piece is straightened; second stage of the experiment: the arcshaped test piece is pulled until the arcshaped test piece is stretched to the specified strain or finally damaged, and the whole test is finished; and calculating according to the tension data and the strain data measured in the linear range of the second stage of the test to obtain the hoop elastic modulus and/or Poisson ratio of the composite pipe.
Preferably, the arcshaped test pieces are ringshaped test pieces at least 2 heights of a composite pipe, each ring is provided with at least 2 arcshaped test pieces, and the total number of the arcshaped test pieces is not less than 4.
Preferably, the width of the arc test piece should not exceed 35mm and should not be less than 20mm, and the gauge length of the arc test piece should not be less than 100mm and should not be more than 200 mm. In order to ensure the transmission of the tensile force, the anchoring length of the two ends of the arcshaped test piece is not less than 30 mm.
Preferably, the adhesive strain gauge includes: the strain gauge is accurately positioned and adhered to the inner surface and the outer surface of the arcshaped test piece, a 1 st strain gauge and a 2 nd strain gauge are respectively adhered to two sides of the middle part of the inner surface of the arcshaped test piece along the longitudinal direction, and a 3 rd strain gauge is adhered to the center position of the outer surface along the longitudinal direction; when the Poisson's ratio needs to be measured, besides the 1 st strain gage, the 2 nd strain gage and the 3 rd strain gage, the 5 th strain gage needs to be transversely pasted at the position, close to the 3 rd strain gage, of the outer surface of the arcshaped test piece, the 4 th strain gage is transversely pasted at the position, corresponding to the 5 th strain gage, of the inner surface of the arcshaped test piece, the strain gage with the gauge length ranging from 5mm to 20mm is preferably adopted, and meanwhile, the gauge length of the strain gage is not smaller than 3 times of the minimum repeated size of the fiber distribution structure of the arcshaped test piece.
Preferably, the oneway hinge is a steel processing component, one end of the oneway hinge is a solid cylinder, and the oneway hinge is fixedly connected with the tensile testing machine; the other end of the wedgeshaped selflocking clamp is a hollow cylinder, an end rod of the wedgeshaped selflocking clamp is inserted into the hollow cylinder, and the wedgeshaped selflocking clamp is connected with the oneway hinge through an inserted steel shaft; the hollow cylinder of the oneway hinge is provided with a notch at two sides of a plane vertical to the steel shaft, and the wedgeshaped selflocking clamp can freely rotate around the steel shaft in the plane (the position of the steel shaft is a hinge fulcrum), so that the arcshaped test piece can be smoothly straightened in the stretching process.
Preferably, the whole tensile test is carried out from the beginning of loading until the test piece is pulled to a preset strain or is damaged, the total time is not less than 30 minutes, the loading mode of the test is displacement control, and the first stage and the second stage of the test adopt different loading speeds; the first stage is a bending control stage, firstly, the distance of a loading head to be moved in the stage is determined according to the difference value between the arc length of an arc test piece between two unidirectional steel hinge shaft positions and the linear distance of the two unidirectional steel hinge shafts at the initial starting moment, and then the loading speed in the stage is calculated under the limiting condition that the loading time in the stage is not less than 5 minutes; the second stage is a stretching control stage, and the loading speed should be reduced to 0.10.2 mm/min.
Preferably, in the first stage and the second stage of the test, all the data such as the tension data and the strain data are continuously recorded by using the data acquisition instrument.
Preferably, the average of the data of the 1 st strain gage, the 2 nd strain gage and the 3 rd strain gage is used for eliminating the centering error of the arcshaped test piece and simultaneously is also used for judging whether the centering error is within an acceptable range, and the centering error of the test can be calculated by the following formula:
in the formula:
B_{y}the outofplane bending index (%) of the arc test piece is expressed, and the increment form is adopted and is only used for error analysis in the second stage;
B_{z}representing a% inplane bending index of the arc specimen;
ε_{1}，ε_{2}，ε_{3}indicating the readings of the 1 st, 2 nd and 3 rd strain gauges, respectively;
ε_{ave}representing the average tensile strain of the arc specimen;
ε_{c}，ε_{t}respectively representing the strain of the outer surface of the arc test piece and the strain of the inner surface of the arc test piece, which are respectively equal to epsilon_{3}And
Δε_{ave}to representAverage tensile strain increment of the second stage of the arcshaped test piece;
Δε_{3}representing the mean increase in tensile strain Δ ε in the second stage_{ave}The corresponding 3 rd gauge reading increment;
B_{y}and B_{z}Preferably within + 5%.
Preferably, the hoop modulus of elasticity and the poisson's ratio of the test piece are calculated as follows:
in the formula:
σ — represents tensile stress (MPa);
frepresents the tensile load (N);
brepresents the arc specimen width (mm);
trepresents the arc specimen thickness (mm);
corresponding to the second stage of test loading (namely the stretching control stage), the tensile stresstensile strain curve basically shows linearity, the slope of the tensile stresstensile strain curve is the annular elastic modulus of the composite pipe, and in order to ensure the reliability of data, the strain increase delta epsilon in the linear range in the tensile stressaverage tensile strain curve is selected_{ave}At least 0.2% of the data between the two points is used to calculate the hoop modulus of elasticity of the test piece, which is the ratio of the corresponding increase in tensile stress to the increase in average tensile strain, as calculated by the following equation:
in the formula:
E_{θ}representing the hoop modulus of elasticity (MPa) of the composite pipe;
Δε_{ave}represents a second stage average tensile strain increase of at least 0.2%;
delta sigmarepresents the mean increase in tensile strain from the second stage, Delta epsilon_{ave}Corresponding tensile stress increment (MPa);
calculation of poisson ratio:
the poisson ratio is the ratio of the corresponding average transverse strain increase to the average longitudinal strain increase, and is calculated by the following formula:
ε_{f}＝ε_{ave}
v_{θx}representing the composite pipe hoop poisson's ratio;
ε_{l}representing the average transverse strain of the arc specimen;
ε_{f}representing the mean longitudinal strain (i.e.. epsilon.) of the curved specimen_{ave})；
ε_{4}，ε_{5}indicating the readings of the 4 th and 5 th strain gauges, respectively;
Δε_{l}expressing and second stage mean tensile strain delta [ epsilon ]_{ave}A corresponding average lateral strain increment;
Δε_{f}expressing and second stage mean tensile strain delta [ epsilon ]_{ave}Corresponding average longitudinal strain increase (i.e., Δ ε)_{ave})。
As a preference, the method is applicable to a composite pipe satisfying the following conditions:
in the formula:
trepresents the thickness of the composite pipe;
drepresents the diameter of the composite pipe;
ε_{u}representing a preset maximum value of the average tensile strain applied in the test or the hoop limit tensile strain of the composite pipe;
ε_{e}representing the second stage mean increase in tensile strain (i.e. Δ ε) used to calculate the modulus of elasticity_{ave}) Taking 0.2 percent;
in addition, in order to avoid the adverse effect of the boundary effect (the effect that the fiber in the arc test piece is cut off at the edge), the test method is suitable for the composite pipe with the fiber layering angle (the included angle between the fiber direction and the axial direction of the pipe) being more than or equal to 70 degrees; when the fiber layering angle is less than 70 degrees, the width of the test piece is preferably increased properly, and the influence of the nonlinearity of the stressstrain curve is considered.
Compared with the traditional straight stripshaped sheet material tensile test, split disc test and internal pressure test method, the arcshaped test piece tensile test method has the advantages that: the test device and the test method are simple to operate, accurate in measurement result and wide in applicability. The characteristics of extensive applicability mainly embody following four aspects: (1) the method is suitable for composite pipes with circular, elliptical or other curved sections; (2) the method has good adaptability to the dispersion of the geometric dimension of the measured composite material winding pipe; (3) the device can be implemented by various types of tensile testing machines or universal material testing machines; (4) in addition to typical wound composite pipes, the hoop modulus of elasticity and Poisson's ratio can be determined for composite pipes made by hand using a wetlaid process or other curved open or closed crosssection composite pipes.
Drawings
FIG. 1 is a schematic view of a curved test piece made of a composite tube according to the present invention.
FIG. 2 is a front view of an arcshaped test piece to which a strain gauge is attached according to the present invention.
FIG. 3 is a side view of an arc test piece of the present invention with a strain gage attached.
Fig. 4 is a schematic view of a oneway hinge according to the present invention.
FIG. 5 is a schematic drawing of the tension of an arc test piece in the present invention.
FIG. 6 is a tensile stressstrain curve of the arc specimen in the tensile test of the present invention.
In the figure: 11 st strain gage; 22 nd strain gage; 33 rd strain gage; 44 th strain gage; 55 th strain gage; 6arc test pieceAn inner surface; 7, the outer surface of the arcshaped test piece; 8, unidirectional hinging; 9wedgeshaped selflocking clamp; 10arc test piece; 11oneway hinge steel shaft; w is the width of the arc test piece; l_{0}gauge length of arc length.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides an arc test piece tensile test method for measuring the hoop elastic modulus and Poisson ratio of a composite pipe, and the specific implementation mode and requirements of the invention are described by referring to figures 16 and taking some examples.
(1) Preparation of arcshaped test piece
The tested arc test pieces 10 are directly cut along the circumferential direction of the composite pipe, specifically, the test pieces need to be taken from annular test pieces at least 2 heights of the composite pipes in the same batch of composite pipe constrained concrete members, each ring is provided with not less than 2 arc test pieces 10, and the total number of the arc test pieces is not less than 4, as shown in fig. 1. In addition, the arcshaped test piece 10 should be cut along the circumferential direction of the composite pipe, and the edge is smooth, so that the adverse effects of the edge effect and the centering error on the test result are reduced as much as possible.
(2) Arc test piece size
In order to control the bending along the width direction (i.e. inplane bending or inplane bending) caused by the centering error, the width w of the arcshaped test piece should not exceed 35mm, and meanwhile, the width of the test piece should not be smaller than 20mm in order to facilitate the pasting of the strain gauge. The scale distance l of the arc length of the arc test piece is considered in consideration of the influence of the outofplane bending of the arc test piece on the linear stretching of the arc test piece and the influence of the clamp pressure on the test section of the test piece_{0}Should not be less than 100mm, and considering the large bending deformation in the initial stage of stretching and the arc length scale distance l_{0}And should not be larger than 200mm as shown in figure 1. In order to ensure the transmission of the tensile force, the anchoring length of the two ends of the arcshaped test piece 10 should not be less than 30 mm.
(3) Preparation of the test
Before the tensile test is started, each arc tensile test piece needs to be numbered, and the geometric data such as the thickness, the width and the like of the test piece are accurately measured and recorded according to the numbers. Then, a strain gauge is pasted on the test piece, specifically, the strain gauge is precisely positioned and pasted on the inner surface and the outer surface of the arcshaped test piece 10, a strain gauge (i.e. the 1 st strain gauge 1 and the 2 nd strain gauge 2) is respectively pasted on the two sides of the middle part of the inner surface (the tension surface in the bending control stage) along the longitudinal direction, and a strain gauge (i.e. the 3 rd strain gauge 3) is pasted on the center position of the outer surface (the compression surface in the bending control stage) along the longitudinal direction, as shown in fig. 2 and 3. When the poisson ratio needs to be measured, besides the longitudinal strain gauge, a 5 th strain gauge 5 needs to be pasted on the outer surface of the arcshaped test piece close to the 3 rd strain gauge 3 along the transverse direction, and a 4 th strain gauge 4 needs to be pasted on the inner surface 6 of the arcshaped test piece along the transverse direction corresponding to the 5 th strain gauge 5, as shown in fig. 2 and 3. Preferably, a gauge length of 5mm to 20mm is used, and the gauge length of the strain gauge should be no less than 3 times the minimum repeat dimension of the fiber distribution structure of the arc test piece 10.
(4) Stretching clamp
Considering the operation simplicity of centering and fastening the test piece, the invention proposes that the wedgeshaped selflocking clamp 9 is adopted to respectively clamp two ends of the arcshaped test piece 10, and the anchoring surface of the clamp needs to meet certain roughness so as to provide enough anchoring force. The wedgeshaped selflocking clamp 9 is connected with the tensile testing machine through the oneway hinge 8.
Because the arcshaped test piece 10 undergoes a long section of outofplane bending deformation at the initial stage of tensioning until the test piece is straightened, the invention designs two unique oneway hinges 8 to respectively connect the wedgeshaped selflocking clamp 9 with the upper end and the lower end of the tensile testing machine, as shown in fig. 5. The oneway hinge 8 is a steel processing component, and one end of the oneway hinge is a solid cylinder as shown in figure 4 and is fixedly connected with the tensile testing machine; the other end is a hollow cylinder, an end rod of the wedgeshaped selflocking clamp 9 is inserted into the hollow cylinder, and the wedgeshaped selflocking clamp 9 is connected with the oneway hinge 8 through an inserted steel shaft; the hollow cylinder of the unidirectional hinge 8 is provided with a gap on each side of the plane vertical to the steel shaft, and the wedgeshaped selflocking clamp 9 can freely rotate around the steel shaft in the plane (the position of the steel shaft is a hinge fulcrum). During the stretching of the arc test piece 10, the wedgeshaped selflocking clamp 9 can rotate freely around the steel shaft, and the arc test piece 10 can be straightened smoothly.
(5) Loading system
Figure 5 illustrates a typical arc specimen tensile test procedure. The whole test process is divided into two stages, namely a bending control stage and a stretching control stage.
The first phase, the bending control phase, occurs at the beginning of the test loading, from the start of the loading until the specimen is straightened, the deformation of the specimen being dominated by bending. In the process, the tensile force of the testing machine is increased slightly, and the absolute values of the strain of the inner surface and the outer surface (namely the tension surface and the compression surface) of the test piece are correspondingly increased.
The second stage, the tension control stage, begins after the specimen is straightened until the arcuate specimen 10 is stretched to a specified strain or eventually fails, and the test ends. In this process, the increase in the film strain of the test piece gradually replaces the increase in the bending strain, and the deformation of the test piece is dominated by the stretching. At the same time, the absolute value of the longitudinal strain on the outer surface (i.e., the pressure receiving surface) of the test piece undergoes a transition from rising to falling.
The tensile test of the whole arcshaped test piece 10 is carried out from the beginning to the moment when the test piece is pulled to a preset strain or is damaged for no less than 30 minutes, the loading mode is displacement control, and different loading speeds are adopted in the two stages. In the first stage, the distance that the loading head needs to move in the present stage is determined according to the difference between the arc length of the arc test piece 10 between two hinge points (namely, the positions of the oneway hinge steel shafts 11) and the linear distance between the two hinge points at the initial starting time, and then the loading speed in the present stage is calculated under the limiting condition that the loading time in the present stage is not less than 5 minutes. After the test enters the second stage, the loading speed should be reduced to 0.10.2 mm/min. In the whole process, all the tension data and the strain data are continuously recorded by using a data acquisition instrument.
(6) Data processing
Fig. 6 shows a typical tensile stresstensile strain curve of an arc test piece in the whole process of a tensile test, wherein the specified tensile is positive, the specified pressure is negative, and the curves of the inner surface 6 (tension surface) and the outer surface 7 (compression surface) of the arc test piece are obviously divided into two stages, namely a bending control stage and a tensile control stage.
The average of the data of the three longitudinal strain gauges can eliminate the centering error of the test piece to a certain extent, and is also a basis for judging whether the centering error is within an acceptable range.
(a) Error analysis
The centering error can be calculated by:
in the formula:
B_{y}the outofplane bending index (%) of the arc test piece is expressed, and the method is only used for error analysis of the second stage (the stretching control stage) in an incremental mode;
B_{z}representing a% inplane bending index of the arc specimen;
ε_{1}，ε_{2}，ε_{3}readings of strain gauges 1, 2 and 3 of fig. 2 and 3, respectively;
ε_{ave}representing the average tensile strain of the arc specimen;
ε_{c}，ε_{t}respectively representing the strain of the outer surface 7 (compression surface) and the inner surface 6 (tension surface) of the arc test piece, which are respectively equal to epsilon_{3}And
Δε_{ave}representing the average tensile strain increase of the second stage of the arc specimen;
Δε_{3}representing the mean increase in tensile strain Δ ε in the second stage_{ave}The corresponding 3 rd gauge reading increment;
B_{y}and B_{z}Preferably within + 5%.
(b) Calculation of the Ring modulus of elasticity
The tensile stress is calculated as follows:
in the formula:
σ — represents tensile stress (MPa);
frepresents the tensile load (N);
brepresents the arc specimen width (mm);
trepresents the arc specimen thickness (mm).
The second stage of the tensile stressstrain curve is basically linear, the slope of the tensile stressstrain curve is the annular elastic modulus of the composite pipe, and in order to ensure the reliability of data, the strain increase delta epsilon in the linear range in the tensile stressaverage tensile strain curve is selected_{ave}At least 0.2% of the data between the two points is used for calculating the hoop modulus of elasticity of the arc test piece, which is the ratio of the corresponding tensile stress increase to the average tensile strain increase, and is calculated by the following formula:
in the formula:
E_{θ}representing the hoop modulus of elasticity (MPa) of the composite pipe;
Δε_{ave}represents an average tensile strain increase of at least 0.2% during the stretch control phase;
delta sigmarepresents the mean increase in tensile strain Delta epsilon associated with the stretch control phase_{ave}Corresponding tensile stress increment (MPa);
(c) calculation of Poisson's ratio
The poisson ratio is the ratio of the corresponding average transverse strain increase to the average longitudinal strain increase, and is calculated by the following formula:
ε_{f}＝ε_{ave}
v_{θx}representing the composite pipe hoop poisson's ratio;
ε_{l}representing the average transverse strain of the arc specimen;
ε_{f}representing the mean longitudinal strain (i.e.. epsilon.) of the curved specimen_{ave})。
ε_{3}，ε_{4}the readings of the 4 th and 5 th strain gauges of fig. 2 and 3, respectively;
Δε_{l}representing the mean tensile strain increase Δ ε over the stretch control period_{ave}A corresponding average lateral strain increment;
Δε_{f}representing the mean tensile strain increase Δ ε over the stretch control period_{ave}Corresponding average longitudinal strain increase (i.e., Δ ε)_{ave})。
(7) Application range of arc test piece tensile test
In order to ensure that the linear range of the tensile stressstrain curve is at least 0.2 percent, the test piece should meet the following conditions:
in the formula:
trepresents the thickness of the composite pipe;
drepresents the diameter of the composite pipe;
ε_{u}representing a preset maximum value of the average tensile strain applied in the test or the hoop limit tensile strain of the composite pipe;
ε_{e}representing the incremental tensile strain in the stretch control phase (i.e. Δ ε) used to calculate the hoop modulus of elasticity_{ave}) And taking 0.2 percent.
For example, when the method is used for testing the glass fiber composite material winding pipe, the ultimate tensile strain can reach about 2%, and when the diameter of the glass fiber composite material winding pipe is 300mm, the following requirements are met:
t≤(0.020.002)×300＝5.4mm
in addition, in order to avoid the adverse effect of the boundary effect (the effect that the fiber in the arc test piece is cut off at the edge), the test method is suitable for the composite pipe with the fiber layering angle (the included angle between the fiber direction and the axial direction of the pipe) being more than or equal to 70 degrees; when the fiber layering angle is less than 70 degrees, the width of the test piece is preferably increased properly, and the influence of the nonlinearity of the stressstrain curve is considered.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (10)
1. A novel test method for measuring the hoop elasticity modulus and Poisson's ratio of a composite pipe is characterized in that an arc test piece is stretched, and the method comprises the following steps: the tested arcshaped test piece is directly cut along the circumferential direction of the composite pipe, and a strain gauge is pasted; two ends of the arcshaped test piece are respectively clamped on the wedgeshaped selflocking clamp; the wedgeshaped selflocking clamp is connected with a tensile testing machine through a oneway hinge so as to realize the free rotation of the arcshaped test piece around the oneway hinge steel shaft in the tensile process; the test comprises two stages in total; first stage of the experiment: under the stretching action, the outofplane bending of the arcshaped test piece is gradually absorbed until the arcshaped test piece is straightened; second stage of the experiment: the whole test is completed after the arc test piece is pulled until the arc test piece is stretched to the specified strain or finally damaged; and calculating to obtain the hoop elastic modulus and/or Poisson ratio of the composite pipe according to the tension data and the strain data measured in the linear range in the second stage of the test.
2. The method of claim 1, wherein the arc coupons are taken from ring coupons at least 2 heights from a single composite tube, not less than 2 arc coupons are taken per ring and the total number of arc coupons is not less than 4.
3. The method of claim 1, wherein: the width of the arc test piece should not exceed 35mm and should not be less than 20mm, the gauge length of the arc test piece should not be less than 100mm and should not be more than 200mm, and the anchoring length of the two ends of the arc test piece should not be less than 30 mm.
4. The method of any of claims 13, wherein the attaching a strain gage comprises: the strain gauge is accurately positioned and adhered to the inner surface and the outer surface of the arcshaped test piece, a 1 st strain gauge and a 2 nd strain gauge are respectively adhered to two sides of the middle part of the inner surface of the arcshaped test piece along the longitudinal direction, and a 3 rd strain gauge is adhered to the center position of the outer surface along the longitudinal direction; when the Poisson's ratio needs to be measured, besides the 1 st strain gage, the 2 nd strain gage and the 3 rd strain gage, the 5 th strain gage needs to be transversely pasted at the position, close to the 3 rd strain gage, of the outer surface of the arcshaped test piece, the 4 th strain gage is transversely pasted at the position, corresponding to the 5 th strain gage, of the inner surface of the arcshaped test piece, the strain gage with the gauge length ranging from 5mm to 20mm is preferably adopted, and the gauge length of the strain gage is not smaller than 3 times of the minimum repeated size of the fiber distribution structure of the arcshaped test piece.
5. The method according to any one of claims 1 to 3, wherein the oneway hinge is a steel processing member, one end of which is a solid cylinder and is fixedly connected with the tensile testing machine; the other end of the wedgeshaped selflocking clamp is a hollow cylinder, an end rod of the wedgeshaped selflocking clamp is inserted into the hollow cylinder, and the wedgeshaped selflocking clamp is connected with the oneway hinge through an inserted steel shaft; the hollow cylinder of the oneway hinge is provided with a notch at two sides of a plane vertical to the steel shaft, and the wedgeshaped selflocking clamp can freely rotate around the steel shaft in the plane, so that the arcshaped test piece can be smoothly straightened in the stretching process.
6. The method of claim 5, wherein the total time of the first stage and the second stage is not less than 30 minutes, the loading mode of the test is displacement control, and the first stage and the second stage of the test adopt different loading speeds: firstly, determining the distance of a loading head to move in the stage according to the difference between the arc length of an arc test piece between two unidirectional steel hinge shaft positions and the linear distance of the two unidirectional steel hinge shafts at the initial starting moment, and then calculating the loading speed in the stage under the limiting condition that the loading time in the stage is not less than 5 minutes; after the test enters the second stage, the loading speed should be reduced to 0.10.2 mm/min.
7. The method of claim 6, wherein all of the tension and strain data is continuously recorded during the first and second stages of the test using a data acquisition instrument.
8. The method of claim 4, wherein the average of the 1 st, 2 nd and 3 rd strain gage data is used to eliminate the centering error of the arc specimen and also to determine whether the centering error is within an acceptable range, and the centering error of the test is calculated by the following formula:
in the formula:
B_{y}representing the outofplane bending index of the arc test piece in an incremental form for error separation in the second stageSeparating out;
B_{z}representing an inplane bending index of the arc test piece;
ε_{1}，ε_{2}，ε_{3}indicating the readings of the 1 st, 2 nd and 3 rd strain gauges, respectively;
ε_{ave}representing the average tensile strain of the arc specimen;
ε_{c}，ε_{t}respectively representing the strain of the outer surface of the arc test piece and the strain of the inner surface of the arc test piece, which are respectively equal to epsilon_{3}And
Δε_{ave}representing the average tensile strain increase of the second stage of the arc specimen;
Δε_{3}representing the mean increase in tensile strain Δ ε in the second stage_{ave}The corresponding 3 rd gauge reading increment;
B_{y}and B_{z}Preferably within + 5%.
9. The method of claim 7, wherein the hoop modulus of elasticity and the poisson's ratio for the arcuate specimen are calculated as follows:
in the formula:
σ — represents tensile stress;
frepresents tensile load;
brepresents the width of the arc test piece;
trepresents the thickness of the arc test piece;
corresponding to the second stage of test loading, the tensile stresstensile strain curve is basically linear, the slope is the hoop elastic modulus of the composite pipe, and the tensile stressaverage tensile strain curve is selectedStrain increase in linear range Δ ε_{ave}At least 0.2% of the data between the two points is used for calculating the hoop modulus of elasticity of the arc test piece, which is the ratio of the corresponding tensile stress increase to the average tensile strain increase, and is calculated by the following formula:
in the formula:
E_{θ}representing the hoop modulus of elasticity of the composite pipe;
Δε_{ave}represents a second stage average tensile strain increase of at least 0.2%;
delta sigmarepresents the mean increase in tensile strain from the second stage, Delta epsilon_{ave}A corresponding tensile stress increment;
calculation of poisson ratio:
the poisson ratio is the ratio of the corresponding average transverse strain increase to the average longitudinal strain increase, and is calculated by the following formula:
ε_{f}＝ε_{ave}
v_{θx}representing the composite pipe hoop poisson's ratio;
ε_{l}representing the average transverse strain of the arc specimen;
ε_{f}representing the average longitudinal strain of the arc specimen;
ε_{4}，ε_{5}indicating the readings of the 4 th and 5 th strain gauges, respectively;
Δε_{l}expressing and second stage mean tensile strain delta [ epsilon ]_{ave}A corresponding average lateral strain increment;
Δε_{f}expressing and second stage mean tensile strain delta [ epsilon ]_{ave}Corresponding average longitudinal strain increments.
10. The method according to claim 1, wherein the method is applied to a clad pipe satisfying the following conditions:
in the formula:
trepresents the thickness of the composite pipe;
drepresents the diameter of the composite pipe;
ε_{u}representing a preset maximum value of the average tensile strain applied in the test or the hoop limit tensile strain of the composite pipe;
ε_{e}represents the second stage average tensile strain increase, taken as 0.2%, used to calculate the hoop modulus of elasticity;
the method is suitable for the composite pipe with the fiber layering angle more than or equal to 70 degrees.
Priority Applications (1)
Application Number  Priority Date  Filing Date  Title 

CN202110366444.7A CN113281166B (en)  20210406  20210406  Test method for measuring circumferential elastic modulus and poisson ratio of composite pipe 
Applications Claiming Priority (1)
Application Number  Priority Date  Filing Date  Title 

CN202110366444.7A CN113281166B (en)  20210406  20210406  Test method for measuring circumferential elastic modulus and poisson ratio of composite pipe 
Publications (2)
Publication Number  Publication Date 

CN113281166A true CN113281166A (en)  20210820 
CN113281166B CN113281166B (en)  20230502 
Family
ID=77276243
Family Applications (1)
Application Number  Title  Priority Date  Filing Date 

CN202110366444.7A Active CN113281166B (en)  20210406  20210406  Test method for measuring circumferential elastic modulus and poisson ratio of composite pipe 
Country Status (1)
Country  Link 

CN (1)  CN113281166B (en) 
Citations (14)
Publication number  Priority date  Publication date  Assignee  Title 

US5431062A (en) *  19940513  19950711  Baratta; Francis I.  Integral bending moment absorber system for mechanical testing of materials 
JP2004279083A (en) *  20030313  20041007  Toray Ind Inc  Bending test method of frp 
CN103163018A (en) *  20130201  20130619  西北工业大学  Fixture for thinwalled tube hightemperature tension test 
CN203241296U (en) *  20130517  20131016  上海大学  Tensile clamp device for longitudinal arc sheet tensile sample of highstrength pipe 
CN103698212A (en) *  20131224  20140402  哈尔滨工业大学  Method for directly measuring circumferential normal anisotropy coefficient of pipe 
US20160033379A1 (en) *  20140731  20160204  Schott Ag  Method and Apparatus for Determining the Fracture Strength of the Margins of Thin Sheets of BrittleFracture Material 
CN105571941A (en) *  20141030  20160511  深圳市信立泰生物医疗工程有限公司  Mold and method for ring hoop tension tests of small polymer pipes 
CN106248277A (en) *  20160722  20161221  中国石油天然气集团公司  A kind of Higrade steel largecaliber spiral submergedarc welded (SAW) pipe residual stress prediction and verification method 
JP2017072483A (en) *  20151007  20170413  大阪瓦斯株式会社  Tensile test method and tensile test tool 
CN206772705U (en) *  20170509  20171219  青岛宇通管业有限公司  Machine clamp is tested in a kind of tubing ring strength test 
US20180143119A1 (en) *  20161123  20180524  Samsung Electronics Co., Ltd.  Evaluating device of flexural property of material, and evaluation method using the same 
CN109187180A (en) *  20180816  20190111  东南大学  A kind of material Poisson ratio measuring method based on biaxial tensioncompression strength 
CN109283052A (en) *  20181031  20190129  中广核研究院有限公司  The circular elasticity modulus of tubing and the measurement method of Poisson's ratio 
CN111398045A (en) *  20200430  20200710  华南农业大学  Internal pressure test device and test method for measuring annular tensile property of fiber reinforced composite material pipe for structural engineering 

2021
 20210406 CN CN202110366444.7A patent/CN113281166B/en active Active
Patent Citations (14)
Publication number  Priority date  Publication date  Assignee  Title 

US5431062A (en) *  19940513  19950711  Baratta; Francis I.  Integral bending moment absorber system for mechanical testing of materials 
JP2004279083A (en) *  20030313  20041007  Toray Ind Inc  Bending test method of frp 
CN103163018A (en) *  20130201  20130619  西北工业大学  Fixture for thinwalled tube hightemperature tension test 
CN203241296U (en) *  20130517  20131016  上海大学  Tensile clamp device for longitudinal arc sheet tensile sample of highstrength pipe 
CN103698212A (en) *  20131224  20140402  哈尔滨工业大学  Method for directly measuring circumferential normal anisotropy coefficient of pipe 
US20160033379A1 (en) *  20140731  20160204  Schott Ag  Method and Apparatus for Determining the Fracture Strength of the Margins of Thin Sheets of BrittleFracture Material 
CN105571941A (en) *  20141030  20160511  深圳市信立泰生物医疗工程有限公司  Mold and method for ring hoop tension tests of small polymer pipes 
JP2017072483A (en) *  20151007  20170413  大阪瓦斯株式会社  Tensile test method and tensile test tool 
CN106248277A (en) *  20160722  20161221  中国石油天然气集团公司  A kind of Higrade steel largecaliber spiral submergedarc welded (SAW) pipe residual stress prediction and verification method 
US20180143119A1 (en) *  20161123  20180524  Samsung Electronics Co., Ltd.  Evaluating device of flexural property of material, and evaluation method using the same 
CN206772705U (en) *  20170509  20171219  青岛宇通管业有限公司  Machine clamp is tested in a kind of tubing ring strength test 
CN109187180A (en) *  20180816  20190111  东南大学  A kind of material Poisson ratio measuring method based on biaxial tensioncompression strength 
CN109283052A (en) *  20181031  20190129  中广核研究院有限公司  The circular elasticity modulus of tubing and the measurement method of Poisson's ratio 
CN111398045A (en) *  20200430  20200710  华南农业大学  Internal pressure test device and test method for measuring annular tensile property of fiber reinforced composite material pipe for structural engineering 
Also Published As
Publication number  Publication date 

CN113281166B (en)  20230502 
Similar Documents
Publication  Publication Date  Title 

Mertiny et al.  Influence of the filament winding tension on physical and mechanical properties of reinforced composites  
Hiel et al.  A curved beam test specimen for determining the interlaminar tensile strength of a laminated composite  
Kaynak et al.  Use of splitdisk tests for the process parameters of filament wound epoxy composite tubes  
US11209112B2 (en)  Fiber composite system and method for pipe reinforcement  
Khorramian et al.  New testing method of GFRP bars in compression  
CN114414380A (en)  Test device and test method for measuring axial tensile property of composite material pipe for structural engineering  
Kharrat et al.  On the interfacial behaviour of a glass/epoxy composite during a microindentation test: assessment of interfacial shear strength using reduced indentation curves  
CN105067437A (en)  Method for testing tensile property of polymer composite strip sample  
CN113252453A (en)  Test device and test method for measuring hoop tensile property of composite material pipe for structural engineering  
CN106596296A (en)  Single fiber interfacial shear strength testing method and device  
CN113281166A (en)  Novel test method for measuring hoop elasticity modulus and Poisson's ratio of composite pipe  
CN217059707U (en)  Measure axial tensile properties's of combined material pipe test device that structural engineering used  
CN105403457A (en)  Method for testing tensile properties of carbon fiber reinforced resin based thinwall composite pipe fitting  
CN110954407A (en)  Method for testing concrete fracture process under action of different water pressures  
Manalo et al.  Testing and characterization of thick hybrid fibre composites laminates  
CN111398045A (en)  Internal pressure test device and test method for measuring annular tensile property of fiber reinforced composite material pipe for structural engineering  
CN203231963U (en)  Beam test device for bonding strength of fiberreinforced composite reinforcement rib material and concrete  
CN212134365U (en)  Internal pressure test device for measuring tensile property of fiber reinforced composite material pipe ring for structural engineering  
CN111537348A (en)  Test device and test method for measuring axial tensile property of largediameter fiber reinforced composite pipe  
CN215218341U (en)  Measure combined material pipe hoop tensile properties's test device for structural engineering  
Mertiny et al.  A methodology for assessing fatigue degradation of joined fibrereinforced polymer composite tubes  
CN214668249U (en)  Test device for measuring axial compression performance of composite pipe for structural engineering  
Clements et al.  Engineering design data for an organic fibre/epoxy composite  
CN108760476B (en)  Composite material creep behavior test fixture and test method  
CN112858025A (en)  Test device and test method for measuring axial compression performance of composite pipe for structural engineering 
Legal Events
Date  Code  Title  Description 

PB01  Publication  
PB01  Publication  
SE01  Entry into force of request for substantive examination  
SE01  Entry into force of request for substantive examination  
GR01  Patent grant  
GR01  Patent grant 